It's an old Dodger Thoughts term. Basically, if you're a pitcher and you fail miserably against a bad hitter (ie, the opposing pitcher), you need to be yanked out of the game ASAP before more damage is done. I believe the term came about because Jason Grabowski was on the Dodgers and he sucked so whenever he got a hit, it meant that the opposing pitcher was having a really bad day or getting tired. It was a signal that the flood gates were about to open (as much as they did in those days).